Holder for the ignitor tip in ignitron rectifiers



E- H. COXE Jan. 24, 1967 HOLDER FOR THE IGNITOR TIP IN IGNITRON RECTIFIERS Filed Nov. 24, 1961' FIG. 2

FIG.

United States Patent ware Filed Nov. 24, 1961, Ser. No. 154,432 1 Claim. Cl. 313-237 This invention relates to improvements in mercury pool gas tubes, especially those of the discontinuous ionization type, and moreover to ignitron rectifiers. In particular, the invention pertains to a new and improved ignitor assembly for an ignitron rectifier.

Ignitrons are special purpose power rectifiers for conversion of alternating current to direct current. The ignitron is designed to pass current during positive swings of the supply current or voltage and to screen out negative half-waves of the supply current or voltage.

All ignitrons include an anode, a mercury pool cathode and an ignitor assembly, the latter including an ignitor rod and tip in initimate electrical connection. The ignitor tip is immersed within and maintained in continuous contact with the mercury cathode. The purpose of the ignitor assembly is to fire the tube when current passes through the ignitor to the mercury pool. Thus, when current flows through the ignitor assembly cathode spots are formed in the mercury pool and the heat generated creates mercury vapor for firing of the ignitron. If the current flow through the ignitor assembly is properly regulated a free cathode spot will be established in-the mercury pool and when established will produce an are which will be transferred to the anode when the voltage is sutficient to support ionization. Thus, the ignitron can be regulated to fire at any chosen time during the halfcycle of anode voltage by means of the ignitor assembly.

Ignitor assemblies are composed of component parts including an ignitor tip and a holder or rod. The ignitor tip is generally made by sintering boron crystals and boron nitride under pressure in a graphite cubicle. This material is then ground to the desired shape and mounted in some fashion or another upon the supporting holder.

Present methods of mounting ignitron tips upon their holder has left something to be desired inasmuch as present ignitor assemblies are subject to frequent replacement. A major factor contributing to the short life of these assemblies is due to the intense heat which is generated each time the arc is struck; which, in an ignitron tube, is struck during some chosen time of each positive halfcycle of anode voltage or current. In a present commercially used ignitor assembly, for example, the ignitor tip is conical shaped and is appended to the terminus of a steel holder by a metal screw passed directly through the holder and into the base of the tip. In such assembly during operation of the ignitron the tip becomes loosened and the base no longer makes proper contact with the holder. As a result the ignitron frequently misfires, the formation of the spot in the mercury pool being premature or retarded. Thus, the ignitor assemblies must be frequently repaired or replaced. Even further, the ignitor tips are often displaced quite easily from the holders even when shipped.

There exists in the art a particular need for a new and improved ignitor assembly, particularly a holder and tip assembly for an ignitron rectifier; and accordingly it is the prime objective of the present invention to supply that need.

The present invention achieves the foregoing and other objectives by producing a new and improved ignitor assembly including a holder and ignitor tip assembly which assures long life and more stable and efiicient ignitron operation. The ignitor assembly comprises a holder upon a terminus of which is rigidly affixed an externally threaded plug or stud, a generally frusto conical shaped ignitor tip and an open end flange member for operative association with the stud and ignitor tip. The flange member is adapted with internal threads for mating With the threaded plug and the open end thereof provides shoulder walls for operative association With the base portion of the frusto conical shaped ignitor tip for holding the tip in substantially axial alignment and in contact with the plug.

T he invention will be better understood in view of the following detailed description presented with reference to the accompanying drawings wherein:

FIGURE 1 is a simplified schematic diagram illustrating an elevational sectional view of an ignitron rectifier;

FIGURE 2 shows in detail a preferred ignitor assembly for use in such rectifier tubes; and

FIGURE 3 shows in detail an even more refined embodiment.

Referring to FIGURE 1 is shown a sectional view of an ignitron tube 10 consisting essentially of a cylindrical vacuum chamber or tank 20 within which is contained an anode 30, a mercury pool cathode 40 and an ignitor assembly 50.

The tank 20 contains spiral guides 21 for circulation of water through the tank walls. Water is introduced into the tank walls through the water intake 22 and is removed through the water output 23, The anode 30 is suitably mounted within the upper portion of the tank 20 and is electrically insulated therefrom. The anode 30 is connected to a circuit through anode lead 31. The mercury pool cathode 40 is located at the bottom of the tank 20 and can be connected to the cathode circuit through cathode lead 41. An ignitor assembly 50 is atfixed within the wall of the tank 20 and is electrically insulated therefrom. An ignitor lead 51 provides for the flow of current through the ignitor assembly 50. The ignitor tip 52 is in contact with and immersed within the mercury pool cathode 40. With a chosen positive anode voltage, an arc will take place between the anode 30 and cathode 40.

FIGURE 2 shows a preferred ignitor assembly for an ignitron rectifier. Thus, upon a terminal end of the holder or rod 50 is secured a peripherally or externally threaded stud or plug 53. Fitted against an end of the plug 53 is'a frusto conical shaped ignitor tip 52 having shoulders 52 and 52 This tip 52 is held snugly against the plug 53, making good electrical connection therewith, by means of the internally threaded female flange member 54, the threads of which mate with the plug 53. The member 54 is further provided with an open end through which can be projected the conical section of the tip 52. Thus, the member 54 is screwed and tightened upon the plug 53 so that the pointed end of the tip 52 projects through the open end of the member 54, the tip 52 being held rigidly in proper position upon the shoulders 52 52 of the tip 52 by pressure of the walls formed at the opening of the member 54.

In FIGURE 3 is shown an alignment for assembly which is an especially preferred embodiment wherein the plug 53 is attached to the holder 50 by welding 53 The base 52 is aligned upon the stud or plug 53 for contact with the base 53 thereof. The internally threaded nut of flange member 54 can be screwed upon the threaded plug 54 so that the tip 52 will be held rigidly in the desired position.

An ignitor tip fabricated pursuant to the embodiment of FIGURES 2 and 3 is admirably suitable for use in ignitron rectifiers for extremely long periods of time without any necessity of replacement; and during which time proper electrical contact is maintained between the tip and the holder so that misfiring of the ignitron rectifier does not occur. Further, these ignitor assemblies can be shipped without elaborate packaging and the ignitor tip not subject to easy displacement from its holder by rough handling.

Some modification can be made in the apparatus described without departing from the spirit and scope of the invention and therefore a full range of equivalents is desired except as limited by the prior art.

Having described the invention what is claimed is:

A mechanically strong ignitor tip assembly essentially free of air gaps for use in an ignitron rectifier consisting essentially of an ignitor holder upon a terminal portion of which is atfixed 'a plug having a base portion and external threads on the entire length, said plug being substantially cylindrical with two ends, solid, of substantially uniform diameter and having good electrical transmission characteristics, said plug having one end affixed to said ignitor holder and the other end providing said base portion; a solid electrical transmitting, generally frusto-conical shaped ignitor tip having flange-like shoulders and a contact base which is adapted to provide essentially airgap free electrical contact with said base portion; an

open end flange member having internal threads for mat- 25 ing with the externl threads of said plug, said flange member engaging the flange-like shoulders of said ignitor tip and securing the contact base compressibly in a direction substantially parallel to the cylindrical axis of said plug against the plug base portion when said flange member is threaded tightly onto said plug to a position substantially in contact with said ignitor holder whereby a solid, compact, unitized ignitor tip assembly is provided essentially free of internal air gaps and through which electrical current may fiow freely with minimum impedance to insure proper firing of an ignitron rectifier.

References Cited by the Examiner UNITED STATES PATENTS 1,313,538 8/1919 Jones 219119 1,718,817 6/1929 Greene 17493 X 1,967,480 7/1934 Ruther 339-400 X 2,107,908 2/1938 Rupp 313171 2,172,185 9/1939 Bangratz 313171 2,685,872 8/1954 Berstler 313-134 X 3,100,832 8/1963 Sosoka et al. 2l9119 FOREIGN PATENTS 723,328 2/1955 Great Britain.

JAMES W. LAWRENCE, Primary Examiner.

GEORGE N. WESTBY, Examiner.

C. R. CAMPBELL, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 300, 674 January 24 1967 Edward H Coxe It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

In the heading to the printed specification, lines 5 and 6, for "Delaware" read Virginia column 1, line 22,

for initimate" read intimate line 65, for "ignitron" read ignition column 3, line 26, for "externl" read external Signed and sealed this 21st day of November 1967.

(SEAL) Attest:

EDWARD J BRENNER Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer 

